Biological Stressor Identification Studies

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Biological impairments impact aquatic communities; therefore, the biological assemblages (e.g., fish, aquatic insects, algae, periphyton) residing in these communities can be used to assess stream conditions and serve as indicators of good or poor water quality. One common measure of biological integrity is an Index of Biotic Integrity (IBI), it is an integrative expression of site condition across multiple metrics that compares the community structure of biological assemblages in a particular stream to that of a high quality (or reference) stream. An index of biological integrity is often composed of at least seven metrics.

In 2002, Maryland began listing waterbodies as impaired for impacts to biological communities in its Integrated Report of Surface Water Quality (IR). A biological impairment is the detrimental effect on the biological integrity of a waterbody caused by an impact, anthropogenic and/or natural, that prevents attainment of the State’s non-tidal water quality standards protecting and supporting the capability of self-sustaining aquatic life.

For each watershed listed as impaired on the IR, the State is to either establish a Total Maximum Daily Load (TMDL) of the specified substance that the waterbody can receive without violating water quality standards, or demonstrate via a Water Quality Analysis (WQA) that water quality standards are being met.

The current methodology used to list watersheds as biologically impaired on the IR uses benthic macroinvertebrate and fish IBIs to indicate that a biological impairment has occurred; however, it does not definitively determine the stressor causing the biological impairment. MDE has developed a Biological Stressor Identification (BSID) analysis that uses a case control, risk-based approach to systematically and objectively determine the predominant causes and sources of degraded biological conditions in impaired watersheds.

The BSID analysis uses the MDDNR MBSS dataset to evaluate habitat, sediment, water chemistry and source parameters in order to determine the potential stressors and anthropogenic sources impacting biological communities in impaired watersheds. Maryland’s BSID analyzes three key groups of stressors: water chemistry, instream and riparian habitat and sediment/flow related; as well as five groups of land use sources: urban, agricultural, barren, anthropogenic and acidic (e.g., acid mine drainage, atmospheric deposition).

The table below lists BSID studies for impaired watersheds. For more information on the methodology used to identify biological impairments in the IR, click here. Depending on when the BSID study was conducted, there are two applicable methodologies. One is the initial version developed in 2009 and the other an updated version in 2014 to include the next round of MBSS data. For more information on TMDLs, click here.